EFFECTS OF HYDROGEN AND FORMATE ON THE DEGRADATION OF PROPIONATE AND BUTYRATE IN THERMOPHILIC GRANULES FROM AN UPFLOW ANAEROBIC SLUDGE BLANKET REACTOR

Degradation of propionate and butyrate in whole and disintegrated gran ules from a thermophilic (55-degrees-C) upflow anaerobic sludge blanke t reactor fed with acetate, propionate, and butyrate as substrates was examined. The propionate and butyrate degradation rates in whole gran ules were 1.16 and 4.0 mumol/min/g of volatile solids, respectively, a nd the rates decreased 35 2nd 25%, respectively, after disintegration of the granules. The effect of adding different hydrogen-oxidizing bac teria (both sulfate reducers and methanogens), some of which used form ate in addition to hydrogen, to disintegrated granules was tested. Add ition or either Methanobacterium thermoautotrophicum DELTAH, a hydroge n-utilizing methanogen that does not use formate, or Methanobacterium sp. strain CB12, a hydrogen- and formate-utilizing methanogen, to disi ntegrated granules increased the degradation rate of both propionate a nd butyrate. Furthermore, addition of a thermophilic sulfate-reducing bacterium (a Desulfotomaculum sp. isolated in our laboratory) to disin tegrated granules improved the degradation or both substrates even mor e than the addition of methanogens. By monitoring the hydrogen partial pressure in the cultures, a correlation between the hydrogen partial pressure and the degradation rate of propionate and butyrate was obser ved, showing a decrease in the degradation rate with increased hydroge n partial pressure. No significant differences in the stimulation of t he degradation rates were observed when the disintegrated granules wer e supplied with methanogens that utilized hydrogen only or hydrogen an d formate. This indicated that interspecies formate transfer was not i mportant for stimulation of propionate and butyrate degradation.